Electrical precipitation apparatus



June 5, 1934. Q T. ur- E1- AL 1,961,658

ELECTRICAL PRECIPITATION APPARATUS I Filed April 9, 1931 2 Sheets-Sheet.1

June 5, 1934. c. T. BUFF El AL ELECTRICAL PRECIPITATION APPARATUS FiledApril 9, 1

2 Sheets-Sheet 2 v Patented June 5, 1934 UNITED STATES 1,961,658ELECTRICAL rascrrrrs'rron APPARATUS Carl Theodor Buff, Berlin-Spandau,and Richard Heinrich, Berlin-Sudende, Germany, assignors, by mesneassignments, to International Precipitation. Company, Los Angeles, Califa corporation of California Application Apr-ill), 1931, Serial No.528,836

. In Germany March 27, 1930 4 Claims.

Our invention relates to electrical precipitation,

apparatus, and particularly to means for feeding the electricalhigh-voltage discharge fields of such apparatus with high-tensionpulsating uni- 5 directional current. 1

The erection of electrical precipitating plants of considerabledimensions, for electrical precipitation of suspended particles fromgases. often encounters difiiculties, since it is, not possible,

owing to the restricted space, to accommodate an individual high-voltagegenerator set for each precipitator unit. The present invention refersto an arrangement by which the above-mentioned difliculties areeliminated.

According to the invention a high-voltage unidirectional currentgenerating system is utilized for feeding several electricalhigh-voltage discharge fields with high-tension pulsating unidirectionalcurrent, said generating system beingconnected to a common high tensionconductor from which the unidirectional current is supplied to thediflferent discharge fields by means of a rotary transfer switch, insuch a manner that these fields are intermittently charged. Forinstance, as in the specific example herein shown, a six-phasetransformer in connection with a bank of thermionic rectifier valves maybe utilized as a high-tension unidirectional current generator. Only asmall space is required for the erection' of such a high-tensiongenerating system.

even for supplying an installation of considerable size with variouskinds of electrical high-voltage discharge fields, such for instance asare employed in precipitators.

The transfer switch is advantageously designed in such a manner" that itpossesses switch arms and associated contact members disposed in onlyone plane. In some cases it may also be convenlent to design thetransfer switch in such a way as to have the switch arms and contactmembers in difl'erent planes. Besides it is convenient to provideadevicefor controlling the speed of the rotary transfer switch. ,It isthereby possible to regulate I at will the duration of the impulses forfeeding the difl'erentprecipitators. If necessary the-c ontactsconnected to the common high tensionjconductor orto the respectivedischarge fields may also be designed so asto be adjustable in orderthat the regulation of duration of impulses inay be eflected by thedisplacement of the contact segments.

A further advantage of the device resides in thepossibility of switchingin a grounded phantom load in place of a discharge field. It is thuspossible to maintain the existing conditions of the system if anoperating field is switched 011.

Finally it is convenient to providespecial regulating resistors forcontrolling the voltage, said resistors being inserted in thehigh-voltage lines leading to the discharge fields. 1

The accompanying drawings show schematically two embodiments of theinvention.

, In these embodiments:

Fig. 1 shows diagrammatically the use of a single rotary switch, an

Fig. 2 shows diagrammatically the use of sev- 'eral rotary switches forsupplying simultaneously difierent impulse frequencies to differentgroups of discharge electrodes.

1 Referring to Fig. '1, 1 denotes a six-phase transformer, to thesecondary coils of which are connected thermionic rectifier valves 3,the output electrodes of which are connected to the 13, 14, 15, 16through the switches 17, 18, 19,

and 20 with the respective precipitators diagrammatically indicated at31. As is customary in 35 such apparatus, the high'tension conductorsareshown as connected to the discharge electrode means of the respectiveprecipitators, while the collectingelectrode means are grounded, thecircuit being completed by grounding the low tension side of thesecondary coils of the transformer, as shown. During the rotation of.the switch 21 about its axis each of the contacts 5, 6, 7 and 8 isconnected successively to its diametrically ODDOSite contact 9, 10, 1iand 12 respectively, so that the several precipitators 31 are intermit-'tently charged by means of unidirectional high potential impulsesdelivered thereto at regular intervalsfrom the common high tensiongenerator. A

Such a generating plant may-be of very small dimensions and yet feed theprecipitator plant sufiiciently with impulses so that effectiveprecipitation is attained.

In the nigh-voltage conductors leading from the transfer switch contacts.9, 10, 11, and 12 to switches 17-20 are inserted the regulatingresistors 22, 23, 24, and 25, respectively, by which it is possible toregulate in the desired manner the voltage of each individualprecipitator. From the high-voltage supply line 16 a conductor 26 leadsto ground, a capacitor 27 and in parallel relation thereto a reactor 28being inserted in this conductor together with a switch 29 which isgenerally open. Should the precipitator 31 fed by the high-voltage line16 be disconnected by means of the switch 20 for any reason, a phantomload can be-substituted for this removed precipitator immediately, inthe form of capacity 27 and reactance 28, by closing switch 29. It isthereby possible to maintain the existing operating condition in thehigh-voltage circuit unaltered, even in the case of a failure of theprecipitator.

Similar devices may also be advantageously utilized for the otherprecipitators 31 fed through the conductors 13, 14, and 15. I I

Such an impulse supply arrangement lends itself with very greateiliciency to multiple-stage electrical cleaning of gases (extraction ofdust), in which it is sometimes desirable to provide differentfrequencies of electric impulses in the respective stages. Fig. 2 showsan arrangement which may be advantageously used for supplyingunidirectional impulses at different frequencies to the successivestages of such an apparatus, from a common source of electrical energy.In this figure, 1 represents, as in Fig. 1, a six-phase transformer, thesecondary of which is connected by way of rectifier valves 33 ofwell-known character to the common high tension conductor 32. Thiscommon conductor is connected by the conductors 34 and 35 respectivelyto the two rotary switches 36 and 37, the arms 38 and 39 of which aremounted on a common shaft 40 driven by an electric motor 41, the speedof which may be controlled in any accepted well-known manner.

' Rotary switch 36 has four fixed supply contacts 42, 43, 44 and 45which are connected by the conductor 34 with the common conductor 32.Opposite to these contacts are placed the normally fixed contacts 46,47, 48 and 49, which latter are connected by way of lines 50, 51, 52 and53 each with an electrical precipitator provided with a suitable numberof electrodes. In order to simplify the illustration only one electricalprecipitator 54 is shown, provided with discharge electrode means 55 andcollecting electrode means 56; said discharge means being connected tothe rotary switch line 50. The collecting electrodes 56 are grounded asusual, the secondary of transformer 1 being also grounded, so that inthis manner the circuit is completed. It will be understood that otherelectrical precipitators may be similarly connected to the lines 51, 52and 53. As in Fig. 1, into each of these connections between theelectrical precipitators and the pertaining switch contacts is connecteda resistance as shown at 50a, 51a, 52a and 53a, for

-connected to the lines 68, 69 and 71.

cerned. By rotatably adjusting this contact group the duration of thecontact between these. contacts and arm 38 can be adjusted, and thus itis possible to adjust the duration of each impulse transmitted to theelectrodes between a maximum and a minimum.

Rotary switch 37 whose arms rotate in a plane parallel to that in whicharms 38 rotate is provided with a four-armed rotor 39 as distinguishedfrom the two arms of the other rotor 38. The contacts 60, 61, 62 and 63of this switch are connectedto common conductor 32 by the conductor 35.These contacts cooperate through the arms of said rotor with contacts64, 65, 66 and 67 which are respectively connected by lines 68, 69, 70and -'ll with the individual electrical precipitators of another group.Also in this case for simplicitys sake only one precipitator of thisother group is shown, namely 73, whose discharge electrodes 72 areconnected by way of conductor 70 to contacts 66 and whose collectingelectrodes 74 are grounded but it will be understood that additionalelectrical precipitators may be similarly The gas stream to be purifiedpasses in the direction of the arrow '75 in series through thetwoprecipitators 54 and 73. In the first precipitator 54 these gases maybe subjected to a pulsating unidirectional current of twenty-five pulsesper second. Thence they pass into the second precipitator 73 whoseelectrodes are supplied with a pulsating unidirectional current ofdouble the above number of impulses per second. In this manner thesuspended material contained in the gases is subjected successively tounidirectional impulses of different frequencies in accordance with therequirement for most efllective precipitation. It will be understoodthat the other precipitators of the respective groups may likewise beconnected for passage of gas therethrough in series, so that the gaspasses in each case first through a precipitator of one group and thenthrough a precipitator of the other group.

The selection of the proper frequency of impulses depends upon thenature of the gases to be cleaned. If for instance dry gases areinvolved, the suspended particles of which possess an insufficientelectrical conductivity, one proceeds advantageously by feeding thefirst cleaning stage with unidirectional current of lower pulsationfrequency than the following stages. It is thereby possible, by reducingthe frequency of pulsation of the unidirectional current, to presentalmost completely the occurring of flashovers, which unfavourably actupon the degree of extraction of dust, in the first stage. By means ofionization of the gas its conductivity is increased. The gasconsequently will cause flash-overs to occur to a smaller extent in thefollowing cleaning-stages. It is therefore possible to now feed thefollowing stages with a unidirectional current of a higher rate ofpulsation than those of the first stage. For instance it has provenadvantageous to supply to the first cleaning stage a unidirectionalcurrent of about 25-50 pulsations per second and to the next cleaningstage a unidirectional current of more than 50 impulses per second. H

A condition of too strong an ionization may thereby occur, so that thenext cleaning stages consume too much energy. In this case it ispreferable to again feed the last fields of the cleaning system withunidirectional current of a lower number of impulses.

Should the cleaning of cases be involved, the

dust particles of which possess from the beginning a good electricalconductivity, it is convenient to feed the first field with pulsatingunidirectional current of a higher number of pulsations and the nextfield with unidirectional current of a lower number of pulsations inorder to prevent in this way the current consumption in the second andin the following fields from becoming too great asa result of the highionization. Owing to the fact that the number of impulses of theunidirectional current corresponding to the condition of the gas ischosen-for each cleaning stage it is possible to obtain in every casethe most favourable current consumption and separation efiect.

We claim as our invention:

1. In electrical precipitation apparatus including a plurality of unitseach comprising com plementary discharge and collecting electrodes, acommon source of high tension unidirectional current, parallel circuitsconnecting said source of current across the electrodes of said units,said circuits including means for independently connecting periodic highvoltage impulses of a predetermined frequency and duration to separategroups of said units.

2. In electrical precipitation apparatus including a plurality of unitseach comprising complementary discharge and collecting electrodes, saidunits being connected'for the flow of gases therethrough in series, acommon source of high tension unidirectional current, parallel 'circuitsconnecting said source of current across the electrodes of said units,said circuits including means for independently connecting periodic highvoltage impulses of a predetermined frequency and duration to separategroups of said units.

3. In electrical precipitation apparatus, a plurality of electricalprecipitators each provided with discharge electrode means andcollecting electrode means, a high voltage unidirectional currentgenerator, a common high tension conductor connected to the high tensionside of said tor, each switch having a plurality of fixed contacts, andeach switch having a rotary contact element cooperating with thepertaining fixed switch contacts, and having a number of contactsdifferent from the number of contact members possessed by the remainingrotary switch.

elements, connections between the fixed contacts of each switch and thedischarge electrode means of a desired number of said electricalprecipitators, to permit the intermittent supply of unidirectionalcurrent impulses of a different frequency to the discharge electrodemeans con-- nectedto the several switches, to produce intermittentelectrical discharges between the electrodes of said precipitators, eachat a frequency adequate to the condition of the suspended materialpassing through the particular precipitator.

4. In electrical precipitation apparatus, a plurality of electricalprecipitators each provided with discharge electrode means andcollecting electrode means, a. high voltage unidirectional currentgenerator, a common high'tension con ductor connected to the hightension side of said generator, a plurality of separate conductorsconnected to the discharge electrode means of the respectiveprecipitators, arotary switching device operable to successively andseparately connect said common conductor to the respective separateconductors so as to intermittently supply' high voltage impulses to thedischarge electrode means of the respective precipitators at a frequencycommensurate with the characteristics of the gas and suspended materialto be passed therethrough, a plurality of shunt paths connected to therespective separate conductors and each provided with electricalresistance means and capacity means, and switch means for opening andclosing the respective shunt paths, so as to permit substitution of aphantom load for any precipitator which is not in operation. I

CARL THEODOR BUFF.

RICHARD HEINRICH.

